The present invention relates generally to a switch, and in particular to a dual-circuit switch having an overload protection mechanism for operation safety.
A switch is operable between an ON (connected) state and an OFF (disconnected) state for control of power supply or electrical signal transmission. For a power switch, overheating and burning caused by overload resulting from undesired shorting is one of the major concerns of operation safety. Some switches available in the market are provided with safety mechanism that automatically cuts off power supplied therethrough in order to eliminate the potential risk of overheating and burning. Such switches, however, have complicated structures, making costs high and manufacture difficult.
The electricity system of some areas, such as Europe, is a dual-circuit system comprised of two electrical circuits individually and independently supplying power to an electric appliance. With the conventional overload protection mechanism, when an overload occurs, it is very likely that only one of the two circuits is open while the other one still maintains the electrical supply. This leads to some disadvantages:
(1) Since the power supplied through the switch is maintained by the circuit that is not broken by the overload protection mechanism, risk caused by overloading of the electrical appliance to which the power is supplied cannot be properly controlled.
(2) Operators that intend to resume supply of electricity by release the overload protection mechanism may be electrically shocked if the circuit that is still maintained is not cut off first.
(3) If the circuit that is open due to overload is not timely resumed its operation condition, power supplied to the electrical appliance through the switch may not be sufficient to properly operate the electrical appliance and thus causing undesired problems.
It is thus desirable to have a dual-circuit switch structure having an overload protection mechanism that overcomes the above problems.
An object of the present invention is to provide a dual-circuit switch comprising an overload protection mechanism that operates to opens both circuits simultaneously in order to completely cut off power supplied through the switch.
Another object of the present invention is to provide a dual-circuit switch comprising an overload protection mechanism that ensures operation reliability in cutting off power supplied through the switch and eliminates incorrect operation caused by material fatigue.
A further object of the present invention is to provide a dual-circuit switch comprising an overload protection mechanism that can be adjusted to provide best response of the overload protection mechanism.
To achieve the above objects, in accordance with the present invention, there is provided a switch comprising a casing inside which two electrically isolated circuits are arranged. Each circuit comprises first and second conductive blades fixed inside the casing. A conductive strip made of a material that bends when subject to a temperature rise is fixed to the first blade and has a free end. A conductive plate is arranged inside the casing and in electrical connection with the second blade and movable between an engaged position where the conductive plate engages the free end of the conductive strip to form an electrical connection between the first and second blades and a disengaged position where the conductive plate disengages from the conductive strip to electrically disconnect the second blade from the first blade. When an overload occurs, an excessive current flows through the conductive strips, causing the strips to bend from a normal operation condition to a breaking condition that separates the conductive strip from the conductive plate. A coupler made of insulation material is coupled between the conductive strips to ensure both conductive strips move to the breaking condition at the same time. A leaf spring is pivoted between the casing and one of the conductive strips to retain the conductive strips in the breaking condition until the conductive strip is manually forced to the normal operation condition to ensure operation reliability. The leaf spring is pivotally connected to the casing via a bolt that allows for adjustment of the leaf spring with respect to the conductive strip.